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FF: Forks New Coilover for Girdraulics



hadronuk

Well Known and Active Website User
VOC Member
#1
I have been talking to a suspension specialist (not AVO) about the possibility of their making a coilover unit that will fit Girdraulics in place of the original damper.
They think they can do it and have asked for more detailed information about available space etc.
But before we go any further, I would greatly appreciate some feedback so I can see if there is some demand.
Two main questions:
  • Would you be interested in buying such a unit?
  • What benefits, specifically, do you think a coilover would give?
I would particularly appreciate comments by racers who have experience of using Girdraulics with a coilover.
Am I right in thinking the Thornton/Works Performance rear coilover fitted the front if a shorter spring was used?

Also, if there is already a supplier, I really need to know!
 

ray vinmad

Well Known and Active Website User
VOC Member
#2
I have been talking to a suspension specialist (not AVO) about the possibility of their making a coilover unit that will fit Girdraulics in place of the original damper.
They think they can do it and have asked for more detailed information about available space etc.
But before we go any further, I would greatly appreciate some feedback so I can see if there is some demand.
Two main questions:
  • Would you be interested in buying such a unit?
  • What benefits, specifically, do you think a coilover would give?
I would particularly appreciate comments by racers who have experience of using Girdraulics with a coilover.
Am I right in thinking the Thornton/Works Performance rear coilover fitted the front if a shorter spring was used?

Also, if there is already a supplier, I really need to know!
Was the lug on the front of the Head Clip designed with the thought of continuously supporting the weight of the machine after 60 years use?
 

vibrac

Well Known and Active Website User
VOC Member
#3
the one on my Brampton Alphabet twin copes but at the top it retains the tapered hole fixing and at the bottom the spring anchor is reinforced with plates from the head lamp lug
Of course the handling on Bramptons was good before I fitted which is why I took the Girdralics off a long time ago (so long that I paid £100 for the girders:cool:) Now with this unit the front has even better handling.
1542124679463.png
 

hadronuk

Well Known and Active Website User
VOC Member
#4
Was the lug on the front of the Head Clip designed with the thought of continuously supporting the weight of the machine after 60 years use?
Good point. But it should have been designed bearing in mind that it could be subject to some substantial shock loads when the damper bottoms out. And the original damper bottomed out much harder than a modern damper with a rubber bump stop.
 

highbury731

Well Known and Active Website User
VOC Member
#5
In principle, I like the idea of a front coil-over, to go with a rear one.... Gets rid of wearing parts and eliminates a source of stiction.
Where to AVO stand wrt front coil-over? Is a different supplier needed?
Paul
 

hadronuk

Well Known and Active Website User
VOC Member
#6
Because of tight clearance where the damper passes through the top link, the coilover has to be "upside down" to put the spring at the bottom. This cannot be done with the type of damper the AVO Vincent range is based on.
 

davidd

Well Known and Active Website User
VOC Member
#7
  • Would you be interested in buying such a unit?
  • What benefits, specifically, do you think a coilover would give?
Rob,

I think the front coil over is an excellent way to go. I would not be in the market as I purchased Works Performance units for any future needs.

For racers, there is an obvious improvement in weight reduction and simplicity. You get rid of a lot of parts.

The front coil overs seem to deliver a better ride. Carlteton Palmer has done a comparison and he far prefers the coil over to the twin springs. I suspect this is due to the different motion ratio of the "A" arm type suspension that the bottom link provides as opposed to the spring box attachments, but I do not have any number comparisons.

I have determined that the FF1 is strong enough for racing. I don't know about street use. I had someone competent do the math and he was OK with it. He asked if it had been done before and I replied it had. John Renwick used this mod on several of his racers successfully. I always buy a new FF1 because the racer bits I start with are always short on parts. I feel it is good insurance. The FF1 could be made out of 7075 or even steel.

The Works Performance damper works well for the front coil over because it is upside down.
500 03.GIF
Patrick uses them front and rear and I have not talked to him about his set up, but it looks similar to mine. The fork is at full extension and it clears the top link.
DSCN2421.jpg
Our own Peter Barker was kind enough to thread this for me when he was last visiting. This was 6"to the top of the thread from the lower perch, if I remember correctly. I prefer using a short spring, but I was unable to get exactly what I wanted, so I settled for the 6.8" spring, 120 lbs., inside diameter 1.75", 0.262 wire diameter, 8.3 coils, 4.63" total deflection. I had to compress it to 6" to install the spring. I would consider an additional inch of thread, or threading to the top, which is more convenient.
DSCN2454.jpg
The photos shows the fork at full droop and there is plenty of clearance. If I were making springs I would make 6" long springs for this use mostly because a longer than 6" spring does not yield any benefit. The top spring perch on this is a short one. The short perches need a lock ring. Works shifted to the long top perch, which does not need a lock. It is also much easier to install a longer spring with the longer perch, because you can start the long perch on the body thread before it hits the spring.
DSCN2424.jpg
I have not tested the 120 lbs. springs so I can't give any information on them. Carleton runs 150 lbs. on his open D Shadow, but he says it at 150 it is a solo bike and cannot handle 2 up well. Works made a 100 lbs. spring that was 5.8" long.

David
 

hadronuk

Well Known and Active Website User
VOC Member
#9
For racers, there is an obvious improvement in weight reduction and simplicity. You get rid of a lot of parts.
The front coil overs seem to deliver a better ride. Carlteton Palmer has done a comparison and he far prefers the coil over to the twin springs. I suspect this is due to the different motion ratio of the "A" arm type suspension that the bottom link provides as opposed to the spring box attachments, but I do not have any number comparisons. David
David, thanks very much for your very useful and detailed reply. From studying Girdraulics, I thought the coilover might give less friction and more linear springing that made better use of the available travel.
But feedback from those that have actually tried it beats all theory!
Rob
 

timetraveller

Well Known and Active Website User
VOC Member
#10
Just be careful with trying to use all the travel. It will depend upon what that means but as recently as yesterday the solution to a problem with travel on the JE steering heads has become clear. One of our members is just fitting his kit and is having trouble with the mudguard hitting the front exhaust pipe nut. This was a problem that John Emmanuel warned me about early on as he had that problem. What became clear yesterday is that if one tries to use more that about three inches of total movement then either the bottom link is too far down at the front and/or too far up on full compression with the collision between exhaust nut and the top link very near to the handlebars. I, only now, understand why John was having problems while almost no one else has had the same problem. John had a special front damper and my guess is that it allowed more travel than the AVO. The member with the problem is using a damper with lots of travel and no bump stop and my guess is that changing that will solve his problem.
 

davidd

Well Known and Active Website User
VOC Member
#11
Rob,

You are certainly welcome. I think Carleton has 3 years of riding on his stock Series D Shadow coil over and Patrick has 4 plus years on the Flash racer. It was Carleton who surprised me by indicating that the front coil over ride seemed superior to the spring boxes.

The Works Performance damper I measured years ago had 2.85" travel to the snubber and a .25" added travel from the squish of the rubber bumper. All of those units were custom CNC builds and there might have been some travel variation over the years, but it does not appear to have amounted to much.

David
 

bmetcalf

Well Known and Active Website User
VOC Member
#12
I saw Carleton’s bike last year, but I don’t remember that it didn’t have the springboxes. Has he taken them off? I’d be tempted to retain them w/o springs to keep the original look.
 

greg brillus

Well Known and Active Website User
VOC Member
#14
A local friend of mine has installed two of the same coilovers that I used on the race bike on his Comet. The ones I used had the two pivot centers at 270 mm apart. He is using the same ones but they are 250 mm centers, and he has made some springs of different spring rates at around 6 inches long. I remember the ones on the racer to be about 300 Lb's on the rear and about 170 or so on the front, this with a fully sprung rear seat. After last weekends racing, we had changed the wheels/tires from 19" to 18" with a 130 mm cantilever type rear tire, and changed the front and rear brake linings as per David's recommendation. Phil said the handling and the brakes had improved very much, and he felt that the bikes handling was very similar to a modern sports bike. I always felt that the suspension on that bike to be excellent and very comfortable, the front end to be very fluid in its movement and behavior. A coilover on the front is a huge improvement over the standard set up. A couple of observations...........they cannot be installed as easily as the shock absorber on it's own, because you cannot compress it to install it. You need to remove the upper fork blade spindle to install/remove it. The shocker on the racer was 270 mm centers this with the Modified steering stem and short type lower eye bolts..........If longer eye bolts had been used the rear lower centre of the upper link would have fouled on the spring ........This is why the spring needs to sit lower on the unit. A 250 mm centres unit would probably cover both types of steering stem but has less available travel. It needs to be set up so as to position the lower link at the right angle before any weight is put on it. The issue of the guard/stay hitting the exhaust can occur if the bike has say a 21" front wheel and if the lower stay is the longer one .........This needs to be moved forward either with a shorter stay or a similar mod.............Just as a point of interest..........For the guard to actually hit the exhaust, it would need the steering to be at that angle and with the suspension very much compressed ...............I feel it would be nearly impossible to duplicate that under any normal riding condition short of the bike nearing a very bad incident ...........Lastly......... I would certainly be checking that the fork blades aren't bent as this too will move it all to the rear, surprising how many bikes may have bent blades and the owner doesn't even know.
 
Last edited by a moderator:

Albervin

Well Known and Active Website User
VOC Member
#18
the one on my Brampton Alphabet twin copes but at the top it retains the tapered hole fixing and at the bottom the spring anchor is reinforced with plates from the head lamp lug
Of course the handling on Bramptons was good before I fitted which is why I took the Girdralics off a long time ago (so long that I paid £100 for the girders:cool:) Now with this unit the front has even better handling.
View attachment 24809
That looks suspiciously like my unit Tim. Who made it for you?
 


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